The invention relates to a process for the preparation of modified polyphenylene ether or related polymers and to the use thereof in modified high temperature rigid polymers of vinyl substituted aromatics. More particularly the invention relates to an improved process for the preparation of modified polyphenylene ether or structurally related polymers by capping the residual free hydroxy groups in such compounds by reaction with an acid derivative.
Blends of polymers of vinyl substituted aromatics and poly(2,6-dimethyl-1,4--phenylene ether), furtheron to be indicated by PPE, or structurally related polymers and more particularly blends of polystyrene and PPE have been aimed at for a long time.
However, the polymerization of vinyl substituted aromatics in the presence of PPE was found to be prohibited or inhibited, which causes lower polymerization yields of the vinyl substituted aromatic monomer and more particularly when the PPE is used in a large amount there are some cases where the polymerization does not progress at all. Accordingly, no substantial polymerization could be progressed unless the PPE was used in an amount as small as possible to make the concentration of the vinyl substituted aromatic compound higher.
This phenomenon was especially observed in the case where a vinyl substituted aromatic, and more particularly styrene, was polymerized in an aqueous dispersion in the presence of PPE and optionally a rubber component. Several processes were proposed in the past such as those described in Japanese patent application No. 22069/67; Dutch patent application No. 6617529; French patent No. 1,551,503, using large excesses of styrene as to the PPE.
A common feature of all these processes was that in order to decrease the styrene content of the polymerization product, it was necessary to lower polymerization yield. In the case of polymerization of e.g. styrene in a suspension system there was observed a phenomenon, that even if the styrene content of the polymerization is intended to be decreased by lowering the polymerization yield, a large amount of unreacted styrene remains in the polymerization product.
The unreacted monomer relatively high in boiling point, which was contained in such beads, was found to be difficultly removed by drying, with the result that a moulded article obtained from the polymerization product was greatly injured in appearance and was also deteriorated in physical properties.
In order to avoid these disadvantages, several remedies were proposed in the past such as described in e.g. U.S. Pat. No. 3,862,263, proposing a process, in which a relatively small amount of a styrene compound is substantially completely graft polymerized on PPE, optionally mixed with an elastomeric polymer, and as described in U.S. Pat. No. 4,287,321 disclosing the preparation of PPE-poly(vinyl aromatic) compositions by oxidatively coupling a phenol dissolved in a basic reaction medium, comprising a vinyl aromatic compound in the presence of a manganese chelate catalyst, selectively extracting base-reactive by-products, and then thermally polymerizing the vinyl aromatic compound.
As another remedy to avoid the hereinbefore described difficulties, processes were proposed for capping the starting PPE by conversion of the remaining free hydroxyl groups in said PPE with a material capable of reacting therewith to form inert substituents in a mutual solvent such as aromatic solvents like toluene, benzene.
Typical examples of such capping agents include acid halides, acid anhydrides or ketenes as disclosed in e.g. European patent applications Nos. 0261574 and 0264623 and U.S. Pat. Nos. 4,048,143; 4,189,417; 4,156,773; and 4,165,422.
Although this capping process was known in principle for some time, a rather extensive research for improved and more economical embodiments has still continued, an important part of the efforts being directed to the application of improved alternative capping agents, as appears e.g. from German patent application No. 3238930, U.S. Pat. No. 4,743,661 and the International patent application WO 83/02117.
Although some of the hereinbefore described processes could indeed provide some progress in the art, there remained a strong need for polymer blends which are obtainable by an economically attractive process for polymerization of a vinyl substituted aromatic monomer in the presence of relatively large amounts of PPE, to be incorporated in the final polymer blends, showing the desired improved characteristics such as high temperature rigidity, and more particularly final polymer blends representing interpenetrating networks.
More particularly there is still a need for an economical manufacturing process for the preparation of modified PPE, which can successfully be applied for the manufacture of blends of polymer of vinyl substituted aromatic monomers and said modified PPE in order to get modified high temperature rigid compositions aimed at. With the term "modified high temperature rigid compositions" as used throughout the present specification are meant compositions, which show a higher glass transition temperature (Tg) as compared with conventional compositions and as a consequence a higher Vicat softening point e.g. measured according to Vicat B DIN 53460.